John Lunn wrote:
he said afterwards that within 90 seconds, her arms and her legs and her lungs just stopped working. Her recovery was remarkably quick, like overnight in hospital.
At those temperatures, the body starts to conserve energy, and just plain shuts down. Scares the hell out of me.
What happens in cold water is the blood is redirected to the core ie to the central part of the body the torso, and away from the extremities such as limbs. This means as you described that arms and legs very quickly become non functional through a lack of blood supply and thus oxygen to the muscles. You lose the functionality of fingers and toes 1st (you often hear of survivors telling how they suddenly couldn't us either fingers to do zips or load flares etc or other things that may have helped their situation), rapidly followed by the limbs themselves. As SRM described you then drown for lack of being able to keep yourself afloat. Sometimes people will pass out 1st through lack of blood flow to the brain although I'm not aware the body deliberately shuts the brain down. I rather think the latter happens more when you have life jacket support than when you are unsupported although I can't back this up with any evidence.
The point to be made overall though is hypothermia can take you down very quickly. One minute you could be cold having eg clambered back into the boat and thinking your safe and the next minute you could find yourself unable to sail it through being unable to use your fingers to grip items such as sheets or the tiller, and that's assuming you even get back aboard. The cold deserves a lot of respect and that's where a wetsuit can really save your life.